In general, electric trains are composed such that power from overhead lines is received by a collector, this received power is used to drive an alternating current rotating machine by means of a drive control device that uses an inverter circuit and/or the like, thereby causing the electric train to run. In addition, when a brake is applied to the electric train, a so-called regenerative brake is used that obtains braking power by regenerative operation of the alternating current rotating machine. The regenerative power generated at this time is supplied via the overhead lines or a third rail to other energized trains near this train or the load of this train's cars, and is thereby consumed.
However, during the early morning and/or at nighttime, and/or on quiet lines with few trains in operation, there are times when other trains are not present near this train, and in such cases the regenerative load is insufficient, so the regenerative power generated by regenerative braking cannot be adequately consumed. When the regenerative electric power of this train is larger than the electric power consumed by other trains, the overhead line voltage rises, creating concerns that various equipment connected to the overhead lines could be tripped and/or damaged by the overvoltage.
Accordingly, some inverter circuits provided in electric trains have a voltage detection unit for detecting the overhead line voltage and/or the like (the overhead line voltage or the filter capacitor voltage of the input side of the inverter circuits, for example, corresponding to the overhead line voltage), and in addition, have a primary circuit composition in which an overvoltage control resistance and a switching device that are part of an overvoltage control unit are connected on the input side of the inverter circuits, so that if the overvoltage occurs, exceeding a predetermined value, operation of the inverter circuits are suspended by opening a switch connecting to the overhead lines which results in discharging the electric charge in the filter capacitor with the switching device of the overvoltage control unit as a continuous conduction condition, thereby protecting equipment from overvoltage (for example, see Patent Literature 1).